The present invention relates to exhaust gas recirculation systems in an internal combustion engine, and, more particularly, to an induction venturi in such exhaust gas recirculation systems.
An exhaust gas recirculation (EGR) system is used for controlling the generation of undesirable pollutant gases and particulate matter in the operation of internal combustion engines. Such systems have proven particularly useful in internal combustion engines used in motor vehicles such as passenger cars, light duty trucks, and other on-road motor equipment. EGR systems primarily recirculate the exhaust gas by-products into the intake air supply of the internal combustion engine. The exhaust gas which is reintroduced to the engine cylinder reduces the concentration of oxygen therein, which in turn lowers the maximum combustion temperature within the cylinder and slows the chemical reaction of the combustion process, decreasing the formation of nitrous oxides (NoX). Furthermore, the exhaust gases typically contain unburned hydrocarbons which are burned on reintroduction into the engine cylinder, which further reduces the emission of exhaust gas by-products which would be emitted as undesirable pollutants from the internal combustion engine.
When utilizing EGR in a turbocharged diesel engine, the exhaust gas to be recirculated is preferably removed upstream of the exhaust gas driven turbine associated with the turbocharger. In many EGR applications, the exhaust gas is diverted directly from the exhaust manifold. Likewise, the recirculated exhaust gas is preferably reintroduced to the intake air stream downstream of the compressor and air-to-air aftercooler (ATAAC). Reintroducing the exhaust gas downstream of the compressor and ATAAC is preferred due to the reliability and maintainability concerns that arise if the exhaust gas passes through the compressor and ATAAC. An example of such an EGR system is disclosed in U.S. Pat. No. 5,802,846 (Bailey), which is assigned to the assignee of the present invention.
With conventional EGR systems as described above, the charged and cooled combustion air which is transported from the ATAAC is at a relatively high pressure as a result of the charging from the turbocharger. Since the exhaust gas is also typically inducted into the combustion air flow downstream of the ATAAC, conventional EGR systems are configured to allow the lower pressure exhaust gas to mix with the higher pressure combustion air. Such EGR systems may include a venturi section which induces the flow of exhaust gas into the flow of combustion air passing therethrough. An efficient venturi section is designed to xe2x80x9cpumpxe2x80x9d exhaust gas from a lower pressure exhaust manifold to a higher pressure intake manifold. However, because varying EGR rates are required throughout the engine speed and load range, a variable orifice venturi may be preferred. Such a variable orifice venturi is physically difficult and complex to design and manufacture. Accordingly, venturi systems including a fixed orifice venturi and a combustion air bypass circuit are favored. The bypass circuit consists of piping and a butterfly valve in a combustion air flow path. The butterfly valve is controllably actuated using an electronic controller which senses various parameters associated with operation of the engine.
With a venturi section as described above, the maximum flow velocity and minimum pressure of the combustion air flowing through the venturi section occurs within the venturi throat disposed upstream from the expansion section. The butterfly valve is used to control the flow of combustion air to the venturi throat, which in turn affects the flow velocity and vacuum pressure created therein. By varying the vacuum pressure, the amount of exhaust gas which is induced into the venturi throat of the venturi section can be varied. However, inducing the exhaust gas into the flow of combustion air in the venturi throat may affect the diffusion and pressure recovery of the mixture within the expansion section of the venturi.
The present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the invention, an internal combustion engine is provided with a combustion air supply, an exhaust manifold, and a bypass venturi assembly. The bypass venturi assembly includes a housing having an outlet, a combustion air inlet connected and in communication with the combustion air supply, and an exhaust gas inlet connected and in communication with the exhaust manifold. A venturi nozzle is positioned in communication with the combustion air inlet. The venturi nozzle defines a bypass venturi section therein. The venturi nozzle and the housing define an exhaust gas venturi section therebetween terminating at an induction area. The venturi nozzle has a plurality of through holes in communication with a downstream portion of the exhaust gas venturi section. The exhaust gas inlet terminates at the induction area. A bypass valve is positioned to open and close the bypass venturi section.
In another aspect of the invention, a method of recirculating exhaust gas in an internal combustion engine is provided with the steps of: providing a bypass venturi assembly including a housing having a combustion air inlet, an exhaust gas inlet and an outlet, a venturi nozzle in communication with the combustion air inlet, the venturi nozzle defining a bypass venturi section therein, the venturi nozzle and the housing defining an exhaust gas venturi section therebetween terminating at an induction area, the venturi nozzle having a plurality of through holes in communication with a downstream portion of the exhaust gas venturi section; transporting combustion air to the combustion air inlet; transporting exhaust gas to the exhaust gas inlet and the induction area; and selectively operating a bypass valve to open and close the bypass venturi section and thereby control an amount of exhaust gas inducted at the induction area.